The present invention relates to a method and device for simultaneous monitoring, while a motor vehicle is in motion, of the steering and wheel suspension geometries and the state of balance of rotating parts connected to the kinematic steering linkage of the motor vehicle.
A device for determining steering angle using frequencies is known ("Frequency Investigations of the Steering Deflections Occurring as a Function of the Operating Conditions" from Heider, H.: "Vehicle Steering", VEB Verlag Technik, Berlin, 1970). It serves to provide electro-mechanical classification, registration and indication of the steering angles employed and frequency of occurrence counters. The counts are analyzed by hand after the counters have been read.
The classification of the steering angles takes place by means of electrical switch contacts, a ring of thirty five contacts being fixed to the steering column tube and a moving contact being pivoted jointly with the steering column. Since no fixed contact is allocated to the straight ahead position of the steering column, or of the moving contact, the classification pitch is ten angular degrees in each case.
This scanning system is supplemented by further electrical contacts on the steering gear. These contacts offer the direction of rotation of the steering movements relative to the straight ahead position to the recording mechanism.
Analysis and interpolation of the class frequencies counted on different journeys using the known device provided different distribution curves whose clearly marked maxima were all located in or near the straight ahead position of the steering linkage.
The objective of the invention is to develop a method and device by which both maladjusted or damaged steering or wheel suspension geometries and unbalanced rotating parts connected to the steering linkage can be automatically recognized quickly during a journey and indicated to the vehicle driver.
This objective of the present invention is achieved by sensing the steering angle as a position of the steering linkage relative to the body work of the vehicle. To determine the state of the steering linkage, the steering angles are classified into classes graduated according to steering angle, magnitude and direction. The frequency of occurrence of the classes are counted. The position of the absolute maximum of the class of the steering angle frequency distribution relative to the straight ahead position of the steering linkage is continuously determined and analyzed during the journey as a criteria of the state of the steering wheel linkage. To determine the state of the balance of the rotating parts connected to the steering linkage, the movement of the steering wheel linkage is continuously determined from the sensed steering angle. These movements are continuously analyzed by comparison with specified values producing a criterion of the state of balance of the rotating parts. A warning signal is provided to the driver when the position of the distribution maximum deviating beyond a tolerance range from the straight forward position of the steering linkage is present and in the case when the unbalance of the rotating parts connected to the steering linkage are determined by the comparison.
For determining unbalance, the comparison is between the steering angle variance determined and the variance which is still permissible for the control condition with the parts balanced. Alternatively, the comparison can be between the frequency of the steering linkage vibrations with the rotational speed of, for example, one of the steered wheels. This agreement implies out-of-balance because out-of-balance-induced vibrations in the steering system are imposed by centrifugal force vectors rotating at wheel speed.
The device for carrying out the method includes a sensor for converting the position of the steering linkage relative to the body of the vehicle into a steering angle signal. A classation circuit is provided for dividing the steering angle signals into classes graduated according to the magnitude and direction of the steering angle. A counter allocated to each class records the frequency of occurrence of the class. A first analyzing circuit connected to the counter provides a reset signal to all of the counters when one of a first set of counters has the greatest content and provides a warning signal when one of the counters from the second group has the largest content. This warning signal indicates maladjusted or damaged steering or suspension geometries. A plurality of fixed value memories have a read enable control connected to the classification circuit and contents varying with the class to which they are allocated. The outputs of the fixed value memories are connected to a total memory which instantaneously adds its contents to the value supplied from the read enabled fixed value memory at each counting cycle. The counting memory has a contents which is increased by one at each counting cycle. A second analysis circuit is connected to the total memory and the counting memory for providing a reset signal to both memories when the contents of the counting memory reaches a specified maximum value and for providing a warning signal as an indication of unbalanced rotating parts when the contents of the totals memory containing a specific maximum value.
The classification circuit includes a plurality of comparators each connected to a distinct reference value and the sensor and a plurality of AND gates connected to the outputs of a pair of comparators to produce the classification. The output of the classification circuit causes a cycle of counting in the counting register and transmission of a fixed value from the fixed value memories to the totals memory. The output signal is produced by a voltage divider. A sample and hold circuit is included at the input of the classification circuit and the period is determined by a fixed distance of travel or proportional to the instantaneous speed. The sensor may be a rotational angle signal generator connected to the steering column or a displacement signal generator on the track rod of the steering linkage. The counting registers may be asynchronous electronic counters actuated by the output of a respective AND gate or pulsed time counters controlled by the pulse generator of the sample and hold and an output of a respective AND gate.
In the case of incorrectly adjusted or damaged steering or wheel suspension geometry, and also in the case of different air pressures in the steered tires, the vehicle tends to pull to one side and is involuntarily compensated by the driver steering in the opposite direction. Increased slip of the steered tires, accompanied by a reduction in their guidance capability and increased wear, are the results.
If the steering angle frequency distribution on an incorrectly adjusted steering linkage is determined, the distribution maximum will settle at a position different from the straight ahead position of the steering linkage.
Out-of-balance on rotating parts connected to the steering linkage (wheels, brake discs, drive shafts) leads to vibrations in the steering linkage and contributes substantially to its wear.
Relative to correctly balanced systems, out-of-balance of the rotating parts will lead to increased variance of the steering angles.
A device for indicating an incorrectly adjusted or damaged steering geometry is in fact known (U.S. Pat. No. 3,438,646). In this patent, however, the positions of the wheels relative to the track rod of a steering linkage are directly recorded by means of one inductive sensor each in two ball joints of the suspensions of the steered wheels. These positions are compared with one another by means of a bridge circuit of the inductive sensors. On pressing a button, the vehicle driver can obtain information on the condition of the steering geometry of his vehicle by means of two ammeter scales. Positions of the two scale fingers which deviate from one another indicate damage or incorrect adjustment. Assessment of the indications is left to the vehicle driver. The two sensors are complicated in design, heavily loaded mechanically due to the movement imposed on the wheels by road irregularities and have to be accurately adjusted although fitted at positions which are difficult to access. Indication of any out-of-balance condition which may be present is not possible with this device simply because of the indication inertia and damping of the indicating instruments.
A device for recording out-of-balance using rotating parts connected to a vehicle steering mechanism by means of a sensor attached to a part of the steering linkage is also known (German Pat. No. 2,819,687). This device uses the steering wheel and steering linkage vibrations due to an out-of-balance condition, recorded by a vibration sensor fastened to the steering wheel of a vehicle, as the criterion for the state of balance during balancing of the externally driven wheels on the jacked-up vehicle with the wheel suspensions unloaded. Apart from the fact that the device is only provided for stationary operation, there is no suggestion that this device can be used on the adjustment of the steering gear and the wheel suspensions.
Advantages of the present invention are:
By using a single sensor on the steering linkage and the automatic analysis of the sensor signals, both damage or faults at the steering gear and wheel suspensions and out-of-balance of rotating parts connected to the steering gear can be recognized quickly by the use of appropriate statistical methods, and signalled to the vehicle driver.
It is possible to generate a warning signal which varies according to the cause of the damage and which then permits an accurate fault signal which does not require any assessment.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.